Triphenyl phosphates

ABSTRACT

TRIPHENYL PHOSPHATES IN WHICH AN AVERAGE OF AT LEAST ONE PHENYL GROUP PER MOLECULE IS SUBSTITUTED WITH AT LEAST ONE ALKYL GROUP CONTAINING FROM L-30 CARBON ATOMS HAVE BEEN FOUND TO BE EXCELLENT LUBRICANTS AND FUNCTIONAL FLUIDS HAVING MUCH LOWER POUR POINTS AND HIGHER VISCOSITY INDICES THAN CONVENTIONAL PHOSPHATE ESTERS.

United States Patent 3,780,145 TRIPHENYL PHOSPHATES Robert E. Malec,Birmingham, Mich., assignor to Ethyl Corporation, Richmond, Va. NoDrawing. Filed Feb. 19, 1971, Ser. No. 117,095

Int. Cl. C071? 9/12; C10m 1/46 US. Cl. 260-966 2 Claims ABSTRACT OF THEDISCLOSURE Triphenyl phosphates in which an average of at least onephenyl group per molecule is substituted with at least one alkyl groupcontaining from 6-30 carbon atoms have been found to be excellentlubricants and functional fluids having much lower pour points andhigher viscosity indices than conventional phosphate esters.

BACKGROUND Triaryl phosphates have been used both as lubricants and ashydraulic fluids. They are most useful in stationary turbineinstallations and in mining equipment where a nonflammable fluid isrequired. In the past, fluids such as tricresyl phosphate havepredominated in such use. One deficiency of such fluids is theirrelatively high pour point and low viscosity index. An object of thisinvention is to provide a class of phosphate esters which has a low pourpoint and a high viscosity index.

SUMMARY The objects of the present invention are accomplished byproviding a triphenyl phosphate ester in which an average of at leastone phenyl group per molecule is substituted with a C alkyl group whichpreferably contains a linear alkyl chain of at least 5 carbon atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of thepresent invention is a triphenyl phosphate ester in which an average ofat least one phenyl group per molecule is substituted with at least onealkyl group containing from 6-30 carbon atoms.

In stating that an average of at least one phenyl group per molecule issubstituted with at least one alkyl group containing 6-30 carbon atoms,it is meant that the number of C alkyl-substituted phenyl groups presentin the phosphate ester divided by the number of molecules of phospshateester is at least one. From this, it is apparent that the ester need notbe a single compound but can be, and as a practical matter generally is,a mixture of triphenyl phosphate esters containing varying amounts of Calkyl substituents on the phenyl ester groups in an amount such that anaverage of at least one phenyl group is C alkyl substituted per moleculeof phosphate ester in the mixture.

The preferred phosphate esters contain an average of from 1-6 C alkylsubstituents per molecule of phosphate ester. As above, this is anaverage value determined by dividing the total moles of C alkylsubstituents by the total moles of phosphate ester.

Although good results are obtained with all alkyl groups containing 6-30carbon atoms, an especially useful product is obtained when the alkylgroup has a substantially linear structure. By this, is it meant thatthe preferred alkyl substituents contain linear carbon chains of atleast 5 carbon atoms. Preferably this linear chain is unbranched. Thisis not to say that the alkyl groups need to be normal alkyl groups. Forexample, l-methyl-npentyl is a 6 carbon alkyl containing a 5 carbonlinear alkyl chain. Likewise, l-ethyl-n-hexyl is a 8 carbon alkylcontaining a 6 carbon linear chain. Similarly, l-n-butyl-npentyl is a 9carbon alkyl group containing two 5 carbon linear chains. Some furtherexamples of alkyl radicals containing from 6-30 carbon atoms and one ormore linear alkyl chains of at least 5 carbon atoms are: 1-methyl-n-eicosyl, l-n-pentyl-n-hexyl, 1,1-dimethyl-n-heptyl, n-pentyl,n-hexyl, n-octyl, n-decyl, n-dodecyl, l-methyl-n-nonosyl,l-n-octyl-n-tiidecyl, l-n-heptyl-n-tricosyl, 1- n-butyl-n-undecyl,1-methyl-n-heptyl, and the like.

Although alkyl groups containing from 6-30 carbon atoms are useful inproviding the low pour point and high viscosity index properties of thepresent phosphate esters, it has been found that alkyls containing 6-18carbon atoms are a more preferred group. As above, these preferredalkyls have a structure such that they are substantially linearthat is,they contain linear alkyl chains of at least 5 carbon atoms. Someespecially useful esters within this class are those in which the alkylgroups contain about 6-8 carbon atoms. In other words these are:n-hexyl, n-heptyl, n-octyl, l-methyl-n-pentyl, l-methyl-nhexyl,1-ethyl-n-pentyl, l-methyl-n-heptyl, l-ethyl-n-hexyl,1,1-dimethyl-n-hexyl, and the like.

Another highly preferred embodiment is a triphenyl phosphate in which anaverage of at least one phenyl group per molecule is substituted with analkyl group containing 10-12 carbon atoms and having a linear alkylchain of at least 5 carbon atoms such that the ester contains an averageof from 1-6 alkyl groups per molecule.

As stated above, the preferred esters contain an average of from 1-6alkyl groups per molecule. However, a more preferred embodiment is atriphenyl phosphate ester containing an average of about 5-6 alkylgroups per molecule of phosphate ester wherein the alkyl groups containabout 12 carbon atoms and have a structure such that they contain alinear alkyl chain of at least 5 ca"- bon atoms.

The phenyl phosphate esters of this invention are an ester or mixture ofesters having the formula:

( )m I M:

wherein R represents an alkyl group containing from 6- 30 carbon atoms,and m, n and p are integers selected from 0, 1, 2 and 3. When the esteris a single compound the sum of m, n and p is from 1-9, and when theester is a mixture of different phosphate esters the sum of the averagevalue of values of m, n and p is from 1-6. The alkyl groups representedby R preferably have a linear alkyl chain of at least 5 carbon atoms intheir structure. The more preferred R groups contain from 6-18 carbonatoms.

The phosphate esters are made by conventional methods. For example,phenol can be alkylated with a C olefin using a Friedel-Crafts catalystto give a mixture of alkylphenols containing the required average of atleast one alkyl for each 3 molecules of phenol, and preferably from 1-6alkyls for each 3 molecules of phenol. The alkylated phenol mixturecontaining the Friedel-Crafts catalyst can then be reacted directly withphosphorous oxychloride to form the phosphate ester of this invention orit can be first converted to its alkali metal salt by reaction with analkali metal hydroxide or alkoxide and the salt then reacted withphosphorus oxychloride. These methods of alkylating phenols and formingaryl phosphate esters are well known. The following examples will serveto illustrate how the synthesis can be carried out. All parts are byweight.

Example 1 Viscosity (cs.)

210 F. 5.84 100 F. 42.91 F. 4,650 Viscosity index 81 Pour point, F

Example 2 One mole part of phenol was alkylated with 1.83 mole parts ofdodecene-l using a BF -ether catalyst to provide a mixture ofl-methyl-n-undecylphenols having an average of about 1.83 alkyl groupsper mole of phenol. This was reacted with 0.33 mole of phosphorusoxychloride and 2 grams of aluminum chloride, giving a triphenylphosphate ester having an average of 5.5 l-methyl-nundecyl alkyl groupsper molecule of phosphate ester. This ester mixture had the followingphysical properties:

Viscosity (cs.):

210 F 11 100 F. 96.4 0 F. 6,990 Viscosity index 108 Pour point, F -35Example 3 In a reaction vessel was placed 1.33 mole parts of phenol, asmall amount of BF 'ether catalyst and 1.6 mole parts of a mixture ofolefins containing from about 12- 30 carbon atoms. The olefincomposition used was 81.4% olefin and 18.6% paraflin. Excluding theparaffin, the olefiHS WCI'C 2.46% C6 10, 23.8% C12, C14, C15, 10.9% C18,C20, 8.1% C22, C24: C26, 2.9% C and 1.1% C olefins. The olefins were amixture of alpha-olefins, branched olefins and internal olefins in theratio of about 12222. The mixture was stirred at about -90 C. for anhour. The resultant alkylphenol mixture was reacted with 1.3 moles ofphosphorus oxychloride at 90 C. for an hour to form a phosphate ester. Asmall amount of unreacted phosphorus oxychloride was then distilled outand then 3.5 mole parts of phenol added. The esterification wascompleted by stirring an additional 12 hours at 100200 C. Unreactedphenol was then washed out. Parafiin and other volatiles were distilledout. The product was a triphenyl phosphate having an average of about1.5 alkyl groups per molecule in which the alkyl group contained fromabout 12-30 carbon atoms. The physical properties of the ester were asfollows:

Viscosity (cs.):

210 F. 11.07 100 F. 107.2 Viscosity index 96 Pour point, F.

used in spark ignition internal combustion engines. In this use theyfunction to extend spark plug life. Amounts of from about 0.1 to 0.5theories are used (one theory being the amount required to convert thelead to lead phosphate). They can be used as anti-wear agents in otherlubricant formulations. For example, they are customarily added tosynthetic ester lubricants used in turbojet aircraft engines. In thisuse, amounts of from about 1-5 percent are blended with the esterlubricant together with the other additives normally required such as anan antioxidant (e.g., phenyl-B-naphthyl amine, phenyl-u-naphthyl amine,dioctyl phenylenediamine, etc.), metal deactivators, silicone antifoamagents, and the like.

The present esters have a further quite unexpected property when used asantiwear agents in synthetic ester lubriants. In synthetic esterlubricants, viscosity properties are quite important and, in fact, boththe Air Force and Navy set stringent specifications on viscosity. Forexample, the most recent Air Force specification (MIL-L 27502) requiresa 40 F. viscosity of 15,000 max. It has been found that the presentphosphate esters when compared to the generally used tricresyl phosphatehave very little etfect on viscosity at higher temperatures while at thesame time decreasing the 40 F. viscosity. Thus, use of the presentesters in place of the art-revered tricresyl phosphate additive can bevery beneficial in helping an ester meet the -40 F. viscosityspecification. This is illustrated by the following data in which thesynthetic ester is a trimethylolpropane ester of a mixture of adipic andC aliphatic monocarboxylic acids.

From the above data, it can be seen that the ester of this invention(Example 1) when compared with use of tricresyl phosphate has verylittle effect at 210 F. or F. In fact, if any, the esters of thisinvention give a slightly higher viscosty at these higher temperatureswhich in itself is beneficial. A highly unexpected property of thepresent phosphate esters is their effect on viscosity at 40 F. Here itcan be seen that the ester containing 2 percent tricresylphosphate has a-40 F. viscosity of 13,- 450 cs. whereas the same synthetic esterlubricant containing the same amount of the phosphate ester of Example 1exhibits a 40 F. viscosity of 13,160 cs. This reduction in viscosity at40 F. is quite significant and can mean the dilference between meetingthe specification and not meeting the specification because otheradditives routinely used in synthetic esters such as thephenyl-anaphthyl amine and phenylenediamine type antioxidants are knownto increase the viscosity of the lubricant.

I claim:

1. A triphenyl phosphate ester in which one phenyl group per molecule issubstituted with 13 alkyl groups containing from about 10-12 carbonatoms and having a linear alkyl chain of at least 5 carbon atoms.

2. A triphenyl phosphate ester of claim 1 wherein said alkyl groupcontains 10 carbon atoms and has a linear alkyl chain of 9 carbon atoms,namely, diphenyl(1-methyl-n-nonylphenyl) -phosphate.

References Cited UNITED STATES PATENTS 2,193,252 3/1940 Kyrides 2609662,237,632 4/1941 Ries 260966 X 3,012,057 12/1961 Fierce et al 2609663,553,155 1/1971 Garrett 260966 R ANTON H. SUTTO, Primary Examiner US.Cl. X.R. 25249.8

